The present invention relates to cutting inserts, toolholders, and cutting tools preferably for machining metallic materials.
Aspects of the invention have application to cutting inserts, toolholders, and cutting tools used in rotating tool applications as well as turning applications. Aspects of the invention will hereinafter be described primarily in terms of their use in rotating tool applications, however, persons skilled in the art will appreciate that the description typically applies as well to turning tool applications, except where otherwise noted.
It is often desirable to mount cutting inserts on abutment surfaces of a toolholder that form negative holding angles. This may be done to, for example, facilitate provision of more inserts on a toolholder than might be possible if some other configuration were used, or to facilitate orientation of inserts so that they form negative rake angles with workpieces.
Cutting inserts are often mounted to toolholders via bolts or screws that extend through holes in the cutting inserts and mate with threaded holes in the toolholder. When cutting inserts are mounted on abutment surfaces having negative holding angles, these bolts can be subjected to substantial shearing forces. Accordingly, it is desirable to provide a cutting tool and a toolholder and insert therefor that facilitates mounting of inserts to supporting surfaces having negative holding angles in a manner and via structures for accounting for the high shearing forces.
For purposes of the present discussion, a surface of a cutting insert that supports the insert relative to a surface of a toolholder (or other structure such as a shim attached to the toolholder) is referred to and defined as a “supporting surface”. The surface of the toolholder that abuts the supporting surface shall, for purposes of the present discussion, be referred to and defined as an “abutment surface”.
For purposes of the present discussion, a “holding angle” is a generic term that can refer to either an axial holding angle or a radial holding angle, or both, and is defined as and refers to a characteristic of an abutment surface of the toolholder. By contrast, for purposes of the present discussion, the angle of a supporting surface of a cutting insert that contacts the abutment surface will be referred to and defined as the “held angle”.
In the context of a rotating tool, a negative axial holding angle α is defined for purposes of the present discussion as follows: as shown schematically in FIG. 1A, a bottom surface shall be considered, for purposes of the present discussion, define a “negative axial holding angle” α with a plane PA parallel to and extending through the longitudinal axis of the toolholder T when, for a tool that is designed to cut when rotated in a counter clockwise direction as illustrated in FIG. 1A, when the tool is viewed from the side, an axially extending edge SAE of a plane of the bottom abutment intersects with the plane PA at an upper point UP of the edge SAE surface and slopes downward toward the bottom of the toolholder from left to right to a lower point LP of the edge. In a tool designed to cut when rotated in a clockwise direction (not shown), the axially extending edge of the plane of the bottom surface slopes downward toward the bottom of the toolholder from right to left. By contrast, FIG. 1B schematically shows a bottom surface forming what shall be considered, for purposes of the present discussion, to be a “positive axial holding angle” α wherein an axially extending edge SAE of a bottom surface slopes downward toward the bottom of the toolholder T from right to left from the upper point UP to the lower point LP of the edge of a tool that is designed to cut when rotated in a counter clockwise direction.
In the context of a rotating tool, a negative radial holding angle ρ is defined for purposes of the present discussion as follows: as shown schematically in FIG. 1C, a bottom surface shall be considered, for purposes of the present discussion, define a “negative radial holding angle” with a plane PA parallel to and extending through the longitudinal axis of the toolholder T when, for a tool that is designed to cut when rotated in a counter clockwise direction as illustrated in FIG. 1C, when the tool is viewed from the bottom, a radially extending edge SRE of a plane of the bottom surface intersects with the plane PA at an inner point IP on the edge SRE and slopes rearwardly of the plane PA to an outer point OP. In a tool designed to cut when rotated in a clockwise direction (not shown), the radially extending edge of the plane of the bottom surface slopes forward of the plane. By contrast, FIG. 1D schematically shows a bottom surface forming what shall be considered, for purposes of the present discussion, to be a “positive radial holding angle” wherein a radially extending edge SRE of a bottom surface slopes forward of the plane PA from the inner point IP on the edge SRE toward the outer point OP for a tool that is designed to cut when rotated in a counter clockwise direction.
In the context of a rotating tool, a zero axial or radial holding angle α or ρ is defined for purposes of the present discussion as when the axially extending edge SAE or the radially extending edge SRE lie on or are parallel with a plane PA passing through the longitudinal axis.
In the context of either a rotating tool or a turning tool, a rake angle is the angle of the cutting face of the insert relative to the workpiece. An insert I has a positive rake angle when its cutting face C forms an angle with the workpiece W as shown in FIG. 2A; a negative rake angle when its cutting face C forms an angle with the workpiece W as shown in FIG. 2B; and a zero or neutral rake angle when its cutting face C is perpendicular to the workpiece as shown in FIG. 2C. As seen in FIG. 2D, the geometry of the cutting face C by the cutting edge E can be modified so that a cutting face oriented so that a plane PC of the cutting face is negative or zero with respect to the workpiece can nonetheless have a portion by the cutting edge E that forms a positive angle with the workpiece. An insert arranged to provide a positive rake angle will ordinarily cut a workpiece more easily than an insert arranged to provide a negative rake angle. An insert arranged to provide a negative rake angle will ordinarily be less likely to break than an insert arranged to provide a positive rake angle.
For purposes of the present discussion, the “plane” of a non-planar surface is defined as a plane roughly parallel with or through an average level of the points on the non-planar surface.
According to an aspect of the present invention, a cutting insert comprises two supporting surfaces, four side surfaces between the two supporting surfaces, each side surface of the four side surfaces intersecting with two other side surfaces of the four side surfaces to form four corners, the four side surfaces intersecting with the two supporting surfaces to form, at two of the four corners, four cutting corners, each cutting corner comprising a first and a second cutting edge component, and to form, at two other ones of the four corners, four non-cutting corners, characterized in that each supporting surface comprises a surface portion and an angled supporting surface, a plane of the angled supporting surface intersecting with a plane of the surface portion along a line of intersection and forming a non-zero angle with the plane of the surface portion, wherein the line of intersection on a first one of the two supporting surfaces is substantially perpendicular to the line of intersection on a second one of the two supporting surfaces.
According to another aspect of the invention, a toolholder for a rotating cutting tool comprises a toolholder body having a longitudinal axis, at least one cutting insert receiving pocket in the toolholder body, the at least one pocket comprising at least one bottom surface, the at least one bottom surface being oriented at a negative holding angle, characterized in that the toolholder comprises at least one angled abutment surface in the at least one bottom surface, the at least one angled abutment surface and the at least one bottom surface being oriented at a non-zero abutment surface angle relative to each other, and in that the abutment surface angle is substantially equal to or greater than, and opposite from, a holding angle at which the at least one bottom surface is oriented so that the at least one angled abutment surface is oriented at a substantially neutral or positive holding angle.
According to another aspect of the invention, a cutting tool comprises a toolholder for a rotating cutting tool, comprising a toolholder body having a longitudinal axis, at least one cutting insert receiving pocket in the toolholder body, the at least one pocket comprising at least one bottom surface, the at least one bottom surface being oriented at a negative holding angle, and a cutting insert mounted in the cutting insert receiving pocket, the cutting insert comprising at least one supporting surface facing the at least one bottom surface, characterized in that the toolholder comprises at least one angled abutment surface in the at least one bottom surface and in that the insert comprises at least one surface portion and at least one angled supporting surface in the at least one supporting surface, the at least one angled abutment surface and the at least one bottom surface being oriented at a non-zero abutment surface angle relative to each other, and the at least one angled supporting surface and the at least one surface portion being oriented at a non-zero supporting surface angle relative to each other, the at least abutment surface angle and the at least one supporting surface angle being equal, and in that the abutment surface angle is substantially equal to or greater than, and opposite from, a holding angle at which the at least one bottom surface is oriented so that the at least one angled abutment surface is oriented at a substantially neutral or positive holding angle.